Patent GB-540505-A (GB)
Title: Aircraft speed and drift indicating systems
IPC: G01S1/02
Filed: 1940-06-20
Abstract: 540,505. Radio-navigation aerials. ELECTRICAL RESEARCH PRODUCTS, Inc. June 20, 1940, No. 10621. Convention date, June 24, 1939. [Class 40 (v)] [Also in Group XXXVI] In order to indicate speed and drift of an aircraft, a radio beam is projected towards the surface of the earth at an acute angle below the horizontal plane of the craft and is rotated about a vertical axis. Reflections of the beam are received from the surface of the earth and the difference in apparent frequency between the transmitted and reflected waves is determined. The average value of this difference indicates the actual speed of the craft, while the instantaneous value indicates the drift or actual direction of motion of the craft relatively to the surface of the earth. A transmitter 11, Fig. 3, is connected by a transmission line 12 to a transmitting antenna 16. A receiving antenna 18 is connected by a transmission line 14 to a detector 40. The antennae 16, 18 are aligned on a common axis in the focal line of a parabolic reflector 17, Fig. 4A. The radiated beam is rotated by rotating the reflector 17 by bevel gears 26, 28 driven by the shaft 27 of a motor 30 which also drives a twophase alternator 34 the voltage of which causes a cathode ray oscillograph 36 to make a circular 'trace in synchronism with the rotation of the radio beam. The output of the detector 40 is the beat frequency between the transmitted and reflected waves and is supplied through an amplifier 42 to a cycle counting circuit 44 which supplies to a speed indicating meter 46 a current proportional to the average frequency of the beat note. Beat frequency is also supplied through a transformer 38 to the horizontal deflecting plates of the cathode ray oscillograph 36. For two beam positions there will be no beat note, and the position of these points on the circular trace indicates the drift or angle between the heading of the craft and the actual direction of motion. A handwheel 29 is provided for pointing the antenna system manually. In the antenna assembly shown in Fig. 6 a three-conductor concentric line system is employed comprising tubes 77, 78 and control conductor 83. Energy from the transmitter is carried on the inner surface of the tube 78 and the outer surface of the tube 77 to the transmitting wave guide 72. The tube 77 is continued to the upper surface of the receiving wave guide 74 and the inner conductor 83 extends below this guide. Flanges 100, 102 permit the guides to be rotated and the conductors 77, 78, 83 and tuning units including the tubes 84, 86 to remain stationary. The effective throat lengths of the guides 72, 74 may be adjusted by sliding conducting discs 90 provided with handles 91 longitudinally in the guides. The guides 72, 74 are held in a frame 76, the upper surface 98 of which is flanged and rests between rollers 92. The upper surface carries a bevel wheel 96 which is driven by a bevel gear 97 on the shaft of a motor 70. A streamlined enclosure 99 is provided to free the guides from the drag of the air. In a modification the transmitter and receiver are mounted in extensions of the throats of their wave guides, which are shaped so that only their orifices extend below the lower surface of the craft. In this case slip-rings are provided for the power and output circuit connections. Specification 533,538 is referred to.